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It is known that materials with superior strength and abrasion-resistance may be developed as composite materials by embedding such reinforcing materials as carbon-based fibers, ceramic-based fibers, or ceramic particles in a metal matrix material such as an aluminum alloy. Such metal matrix composite materials can be manufactured by a die-casting machine 100 such as that shown in FIGS. 1 and 2. In a precasting process, a preform 103 is sintered to a desired shape after inorganic fibers or ceramic particles are mixed with water, dehydrated and dried. The preform 103 is placed in a metal mold 101, while a plunger pump 102 is filled with a molten metal 104 of matrix material. Then a piston 105 forces the metal matrix material to infiltrate into the preform in the metal mold to create a metal matrix composite 106. The metal matrix composite may find various industrial applications including in airplanes and automobiles as a high-strength, light-weight composite material containing inorganic fibers or ceramic particles ranging from 10 to 50% by volume.
Such a manufacturing method of metal matrix composite materials has two problems. First, because the metal matrix composite is not formed in a hermetic state, chemical reactions such as decomposition, precipitation and metal oxidation occur during infiltration, leading to deterioration in the strength characteristics of the composite. Also, when hollow particles are used as a filling material, gravity (buoyancy)-induced particle separation may occur during metal infiltration, making it difficult to manufacture composite materials with a high content of hollow particles.
Fiber-reinforced composite wires manufactured through the infiltration of metals into inorganic (carbon, ceramics, metals, etc.) fiber bundles may also find many industrial applications. Fiber-reinforced composite wires are known to exhibit superior characteristics in durability and reliability. To this end, a molten metal must infiltrate into the interfiber spacing and increase the overall metal volume percentage. One process for the production of such fiber-reinforced composite wires of the required quality is described in U.S. Pat. No. 5,736,199, the disclosure of which is incorporated by reference herein.
This continuous infiltration process uses a metal infiltration apparatus 200 as shown in FIGS. 3 and 4. This apparatus is comprised of a pressure chamber 201 and a bath container 203 for a molten metal 202, such as aluminum, aluminum alloy, or copper. The bath container is heated by a heater 204 and is equipped with an entering orifice 205 at a bottom surface 201a of the pressure chamber and an intermediate orifice 207 for passing inorganic fiber bundles through the bath container for metal infiltration. The entering orifice, connected to a bottom surface 203a of the bath container, allows inorganic fiber bundles 210 to enter the bath container. The intermediate orifice extends from a position within the molten metal to a closure member 206 that covers the opening section of the bath container. Furthermore, an exit orifice 208, provided at an upper surface 201b of the pressure chamber, allows the metal-infiltrated inorganic fiber bundles to exit from the pressure chamber.
Referring to FIG. 4, functions of the orifices will be described by taking the entering orifice 205 as an example. The orifice is cylindrical in shape, and the exterior surface of the orifice is covered with a cooling jacket 214. An insertion hole 205b is formed along the central axis of an orifice body 205a and has an inside diameter slightly greater than the outside diameter of fiber bundles 210 that travel upwardly into the insertion hole. A temperature gradient is provided along the orifice such that the temperature is above the melting temperature of the material in the bath nearest the bath container and below the melting temperature farthest from the bath chamber.
A non-reacting gas, such as argon and nitrogen, is introduced into the pressure chamber 201 from a gas supply source 209. Thus, the interior spaces of both the pressure chamber and the bath container 203 are respectively maintained at preset pressures when the fiber bundles are infiltrated by metal.
In the infiltration apparatus having such a configuration, inorganic fiber bundles that are fed continuously from a bobbin 211 are introduced into the bath container by way of the entering orifice 205 and are brought into contact with the molten metal 202. Because the interior spaces of both the pressure chamber and the bath container are pressurized by a gas supplied from the gas supply source 209, the molten metal infiltrates into the interfiber spacing of the inorganic fiber bundles. The metal-infiltrated fiber bundles then leave the bath container 203 by way of the intermediate orifice 207.
While the inorganic fiber bundles travel through the inside of the pressure chamber 201, the molten metal that has adhered to and infiltrated into the inorganic fiber bundles is cooled, so that a part of the metal solidifies within and around the inorganic fiber bundles. Subsequently, a take-up bobbin 213 takes up a fiber-reinforced metal matrix composite wire 212 coming out of the pressure chamber 201 through the exit orifice 208.
The fiber-reinforced metal matrix composite wire thus produced should be impregnated with the metal in the interior as well as the surface of the bundles. However, for certain metal-fiber combinations with poor wetting characteristics, it is difficult to achieve metal infiltration deep into the interfiber spacing of fiber bundles.
Various efforts have been reported for better metal infiltration through improved wetting characteristics by surface-treating inorganic fiber bundles, including thermal CVD (chemical vapor deposition) reactors and vacuum vapor deposition reactors to deposit metal particles on the surface of fiber bundles. These surface treatments are not effective, however, in depositing metal particles deep within inorganic fiber bundles. Additional requirements of these reactors also increase the manufacturing cost of fiber-reinforced composite wires.
Additionally, when the diameter of a fiber-reinforced metal matrix composite wire produced by the above-described continuous infiltration method is reduced, the through holes of the orifices must become smaller accordingly, making it difficult to pass fiber bundles through holes in this method. Also, the walls of the through holes have been made of carbon-based materials such as graphite, which do not exhibit good durability against wear caused by the friction between the walls and the moving wire. If, on the other hand, the walls are made of materials with high resistance against abrasion, the fiber bundles become more vulnerable to breakage within the orifice.
In a first embodiment of the present invention, a method is provided of manufacturing high-strength, light-weight composite materials with a high content of hollow particles. In particular, the method provides a composite material comprising hollow particles with a mean particle size ranging from 10 to 100 xcexcm and a metal as a binding agent. The binding material is placed on top of a layer of hollow particles in a pressurizable container. The binding material is separated from the layer of hollow particles by a heat-resistant filter securely fixed at a position between the two materials. After evacuating the pressurizable container, the binding material is heated until it melts completely. The pressurization of the pressurizable container from above, preferably by injection of an inert gas, forces the binding agent to infiltrate into the spaces between the hollow particles.
Preferably, the hollow particles are either ceramic-based hollow particles, particularly, silas balloons, glass balloons, or alumina balloons, or carbon balloons. Preferably, the binding agent comprises gold, silver, copper, tin, iron, cobalt, nickel, lead, aluminum, or their alloys. Preferably, the heat-resistant filter is a ceramic-based filter, in particular, formed from a mullite-based material.
After the pressurization step, the resulting composite material is cooled to a predetermined temperature. Preferably, the composite material is cooled rapidly to achieve finer metal grains, which improve the strength of the composite material. The metal-based binding agent is charged with the ceramic-based hollow particles at a charging ratio of 50% by volume or greater, thus providing a light-weight, high-strength metal matrix composite.
In a further embodiment of the present invention, a method and an apparatus are provided for the continuous pressure infiltration of wire that facilitates insertion of fiber bundles into orifices, realizes superior workability, and ensures consistent wire quality by preventing breakage in the fiber bundles during the manufacturing process.
More particularly, the surfaces of inorganic fiber bundles are coated with a metal oxide by dipping the fiber bundles in a solution of a hydrolyzable organic metal compound and hydrolyzing and heat-treating the organic metal compound deposited on the fiber surfaces to form the metal oxide. The coated inorganic fiber bundles are passed through continuous pressure infiltration apparatus to infiltrate a molten metal into the fiber bundles.
Because metal oxides in general possess a high degree of affinity with metal, the metal oxide, formed uniformly on the surface of the fibers within the fiber bundles, facilitates the subsequent step of pressure infiltration of a molten metal deep into the inorganic fiber bundles. The combined steps of the pretreatment and the pressure infiltration allow the inorganic fiber bundles to be fully impregnated with the molten metal in the bath container, thus producing fiber-reinforced metal matrix composite wires of the desired quality.
In a further embodiment, the continuous pressure infiltration apparatus is provided with orifices having enlarged diameter sections at the entering ends and also at the exit ends. The enlarged diameter sections allow the fibers to be more readily inserted and guided into the orifices. Also the interior surface of the passageways in the orifices are preferably finished with a mirror finish. The material of the orifices is selected to have a low reactivity with both the molten metal and the inorganic fiber bundles. Preferably, the orifices are formed from stainless steel, tantalum, molybdenum, platinum, tungsten, or sintered zirconia-ceramic-based materials.
In a still further embodiment, a pressure infiltration apparatus is provided with an ultrasonic generator made of a ceramic material that does not react with the molten metal in the bath container. Application of ultrasonic vibrations promotes the infiltration of molten metal within the fiber bundles.